Evolutionary dynamics and temporal/geographical correlates of recombination in the human enterovirus echovirus types 9, 11, and 30

Molecular epidemiology and characterization of enteroviruses detected in cerebrospinal fluid and respiratory samples in Slovenia, 2014-2023

Enterovirus (EV) infections have various symptoms and severe complications, including death. To determine EV prevalence and EV types in Slovenia, data on over 25 000 EV RNA tests for diagnostics and surveillance from 2014 to 2023 were analyzed. Altogether, 3733 cerebrospinal fluid (CSF) and 21 297 respiratory (sentinel and clinical) samples were tested for EV RNA. EV typing was performed on all residual EV-positive CSF samples and on subset of respiratory specimens. Altogether, 1238 samples tested positive for EV RNA: 238 (6.4%) CSF and 1000 (4.7%) respiratory samples. EV-positive patients were predominantly male (p < 0.001). Many EV-positive CSF samples were from infants under 3 months (33.1%), whereas most EV-positive respiratory samples were from children 1 to 2 years old (49.2%). Echovirus 30 (E-30) was most frequent in CSF (33.0%), followed by CV-B5 (13.8%) and E-6 (13.8%). CV-A6 was most frequent in respiratory samples (16.0%), followed by EV-D68 (7.6%) and CV-A5 (7.4%). EV types in CSF and respiratory samples show diverse dynamics, with some outbreaks indicated. A significant difference was found in the EV detection rate between CSF and respiratory samples by age. Various EV types were characterized, showing that some EV types are more neurotropic or cause more severe infections.

Characteristics of enterovirus infection associated neurologic disease associated in a pediatric population in Spain

INTRODUCTION

Enteroviruses are a type of RNA-strained virus with more than 100 different genotypes. Infection can be asymptomatic, and, if any, symptoms can range from mild to severe. Some patients can develop neurological involvement, such as aseptic meningitis, encephalitis, or even cardiorespiratory failure. However, in children, the risk factors for developing severe neurological involvement are not well understood. The aim of this retrospective study was to analyze some characteristics associated with severe neurological involvement in children hospitalized for neurological disease after enterovirus infection.

METHODS

retrospective observational study analyzing clinical, microbiological and radiological data of 174 children hospitalized from 2009 to 2019 in our hospital. Patients were classified according to the World Health Organization case definition for neurological complications in hand, foot and mouth disease.

RESULTS

Our findings showed that, in children between 6 months old and 2 years of age, the appearance of neurological symptoms within the first 12h from infection onset-especially if associated with skin rash-was a significant risk factor for severe neurological involvement. Detection of enterovirus in cerebrospinal fluid was more likely in patients with aseptic meningitis. By contrast, other biological samples (e.g., feces or nasopharyngeal fluids) were necessary to detect enterovirus in patients with encephalitis. The genotype most commonly associated with the most severe neurological conditions was EV-A71. E-30 was mostly associated with aseptic meningitis.

CONCLUSIONS

Awareness of the risk factors associated with worse neurological outcomes could help clinicians to better manage these patients to avoid unnecessary admissions and/or ancillary tests.

Genetic diversity and recombination of bovine enterovirus strains in China

Bovine enterovirus (BEV) consisting of enterovirus species E (EV-E) and F (EV-F) is the causative agent associated with respiratory and gastrointestinal diseases in cattle. Here, we reported the characterization, genetic diversity, and recombination of novel BEV strains isolated from the major cattle-raising regions in China during 2012-2018. Twenty-seven BEV strains were successfully isolated and characterized. Molecular characterization demonstrated that the majority of these novel BEV strains (24/27) were EV-E, while only few strains (3/27) were EV-F. Sequence analysis revealed the diversity of the circulating BEV strains such as species and subtypes where different species or subtype coinfections were detected in the same regions and even in the same cattle herds. For the EV-E, two novel subtypes, designated as EV-E6 and EV-E7, were revealed in addition to the currently reported EV-E1-EV-E5. Comparative genomic analysis revealed the intraspecies and interspecies genetic exchanges among BEV isolates. The representative strain HeN-B62 was probably from AN12 (EV-F7) and PS-87-Belfast (EV-F3) strains. The interspecies recombination between EV-E and EV-F was also discovered, where the EV-F7-AN12 might be from EV-E5 and EV-F1, and EV-E5-MexKSU/5 may be recombined from EV-F7 and EV-E1. The aforementioned results revealed the genetic diversity and recombination of novel BEV strains and unveiled the different BEV species or subtype infections in the same cattle herd, which will broaden the understanding of enterovirus genetic diversity, recombination, pathogenesis, and prevention of disease outbreaks.

IMPORTANCE

Bovine enterovirus (BEV) infection is an emerging disease in China that is characterized by digestive, respiratory, and reproductive disorders. In this study, we first reported two novel EV-E subtypes detected in cattle herds in China, unveiled the coinfection of two enterovirus species (EV-E/EV-F) and different subtypes (EV-E2/EV-E7, EV-E1/EV-E7, and EV-E3/EV-E6) in the same cattle herds, and revealed the enterovirus genetic exchange in intraspecies and interspecies recombination. These results provide an important update of enterovirus prevalence and epidemiological aspects and contribute to a better understanding of enterovirus genetic diversity, evolution, and pathogenesis.

Synergetic association between coxsackievirus A16 genotype evolution and recombinant form shifts

Coxsackievirus A16 (CVA16) is a major pathogen that causes hand, foot, and mouth disease (HFMD). The recombination form (RF) shifts and global transmission dynamics of CVA16 remain unknown. In this retrospective study, global sequences of CVA16 were retrieved from the GenBank database and analyzed using comprehensive phylogenetic inference, RF surveys, and population structure. A total of 1,663 sequences were collected, forming a 442-sequences dataset for VP1 coding region analysis and a 345-sequences dataset for RF identification. Based on the VP1 coding region used for serotyping, three genotypes (A, B, and D), two subgenotypes of genotype B (B1 and B2), and three clusters of subgenotype B1 (B1a, B1b, and B1c) were identified. Cluster B1b has dominated the global epidemics, B2 disappeared in 2000, and D is an emerging genotype dating back to August 2002. Globally, four oscillation phases of CVA16 evolution, with a peak in 2013, and three migration pathways were identified. Europe, China, and Japan have served as the seeds for the global transmission of CVA16. Based on the 3D coding region of the RFs, five clusters of RFs (RF-A to -E) were identified. The shift in RFs from RF-B and RF-C to RF-D was accompanied by a change in genotype from B2 to B1a and B1c and then to B1b. In conclusion, the evolution and population dynamics of CVA16, especially the coevolution of 3D and VP1 genes, revealed that genotype evolution and RF replacement were synergistic rather than stochastic.

Fulminant echovirus 11 hepatitis in male non-identical twins in northern Italy, April 2023

Echovirus 11 (E11) has recently been associated with a series of nine neonatal cases of severe hepatitis in France. Here, we present severe hepatitis caused by E11 in a pair of twins. In one of the neonates, the clinical picture evolved to fulminant hepatitis. The E11 genome showed 99% nucleotide identity with E11 strains reported in the cases in France. Rapid genome characterisation using next generation sequencing is essential to identify new and more pathogenetic variants.

A Novel Dependoparvovirus Identified in Cloacal Swabs of Monk Parakeet (Myiopsitta monachus) from Urban Areas of Spain

The introduction of invasive birds into new ecosystems frequently has negative consequences for the resident populations. Accordingly, the increasing population of monk parakeets (Myiopsitta monachus) in Europe may pose a threat because we have little knowledge of the viruses they can transmit to native naïve species. In this study, we describe a new dependoparvovirus detected by metagenomic analysis of cloacal samples from 28 apparently healthy individuals captured in urban areas of Madrid, Spain. The genomic characterization revealed that the genome encoded the NS and VP proteins typical of parvoviruses and was flanked by inverted terminal repeats. No recombination signal was detected. The phylogenetic analysis showed that it was closely related to a parvovirus isolated in a wild psittacid in China. Both viruses share 80% Rep protein sequence identity and only 64% with other dependoparvoviruses identified in Passeriformes, Anseriformes, and Piciformes and are included in a highly supported clade, which could be considered a new species. The prevalence was very low, and none of the additional 73 individuals tested positive by PCR. These results highlight the importance of exploring the viral genome in invasive species to prevent the emergence of novel viral pathogenic species.

Patterns and Temporal Dynamics of Natural Recombination in Noroviruses

Noroviruses infect a wide range of mammals and are the major cause of gastroenteritis in humans. Recombination at the junction of ORF1 encoding nonstructural proteins and ORF2 encoding major capsid protein VP1 is a well-known feature of noroviruses. Using all available complete norovirus sequences, we systematically analyzed patterns of natural recombination in the genus Norovirus both throughout the genome and across the genogroups. Recombination events between nonstructural (ORF1) and structural genomic regions (ORF2 and ORF3) were found in all analyzed genogroups of noroviruses, although recombination was most prominent between members of GII, the most common genogroup that infects humans. The half-life times of recombinant forms (clades without evidence of recombination) of human GI and GII noroviruses were 10.4 and 8.4-11.3 years, respectively. There was evidence of many recent recombination events, and most noroviruses that differed by more than 18% of nucleotide sequence were recombinant relative to each other. However, there were no distinct recombination events between viruses that differed by over 42% in ORF2/3, consistent with the absence of systematic recombination between different genogroups. The few inter-genogroup recombination events most likely occurred between ancient viruses before they diverged into contemporary genogroups. The recombination events within ORF1 or between ORF2/3 were generally rare. Thus, noroviruses routinely exchange full structural and nonstructural blocks of the genome, providing a modular evolution.

Rhinovirus Infection and Virus-Induced Asthma

While the aetiology of asthma is unclear, the onset and/or exacerbation of asthma may be associated with respiratory infections. Virus-induced asthma is also known as virus-associated/triggered asthma, and the reported main causative agent is rhinovirus (RV). Understanding the relationship between viral infections and asthma may overcome the gaps in deferential immunity between viral infections and allergies. Moreover, understanding the complicated cytokine networks involved in RV infection may be necessary. Therefore, the complexity of RV-induced asthma is not only owing to the response of airway and immune cells against viral infection, but also to allergic immune responses caused by the wide variety of cytokines produced by these cells. To better understand RV-induced asthma, it is necessary to elucidate the nature RV infections and the corresponding host defence mechanisms. In this review, we attempt to organise the complexity of RV-induced asthma to make it easily understandable for readers.

Detection of recombinant breakpoint in the genome of human enterovirus E11 strain associated with a fatal nosocomial outbreak

BACKGROUND

The aim of this study was to characterize the genome of a recombinant Enterovirus associated with severe and fatal nosocomial infection; it was typed as Echovirus 11 (E-11) according to the VP1 gene. Enterovirus infection is generally asymptomatic and self-limited, but occasionally it may progress to a more severe clinical manifestation, as in the case described here. Recombination plays a crucial role in the evolution of Enteroviruses (EVs) and has been recognized as the main driving force behind the emergence of epidemic strains associated with severe infection. Therefore, it is of utmost importance to monitor the circulation of recombinant strains for surveillance purposes.

METHODS

Enterovirus-RNA was detected in the serum and liver biopsy of patients involved in the nosocomial cluster by commercial One-Step qRT-PCR method and the Enterovirus strains were isolated in vitro. The EVs typing was determined by analyzing the partial-length of the 5'UTR and VP1 sequences with the web-based open-access Enterovirus Genotyping Tool Version 0.1. The amplicons targeting 5'UTR, VP1 and overlapping fragments of the entire genome were sequenced with the Sanger method. Phylogenetic analysis was performed comparing the VP1 and the full-genome sequences of our strains against an appropriate reference set of Enterovirus prototypes of the Picornaviridae genera and species retrieved from the Enterovirus Genotyping Tool. Recombination analysis was performed using RDP4 software.

RESULTS

The Neighbor-Joining tree of the VP1 gene revealed that the 4 patients were infected with an identical molecular variant of Echovirus 11 (E-11). While the phylogenetic and the RDP4 analysis of the full-genome sequences provided evidence that it was a chimeric strain between an E-11 and a Coxsackievirus B (CV-B).

CONCLUSIONS

The chimeric structure of the E-11 genome might have contributed to the severe infection and epidemic feature of the strain, but further biological characterizations are needed. The evidence reported in this study, highlights the limit of typing techniques based on the VP1 gene, as they fail to identify the emergence of recombinant strains with potentially more pathogenic or epidemic properties, thus providing only partial information on the epidemiology and pathogenesis of Enteroviruses.

Genomic surveillance of enterovirus associated with aseptic meningitis cases in southern Spain, 2015-2018

New circulating Enterovirus (EV) strains often emerge through recombination. Upsurges of recombinant non-polio enteroviruses (NPEVs) associated with neurologic manifestations such as EVA71 or Echovirus 30 (E30) are a growing public health concern in Europe. Only a few complete genomes of EVs circulating in Spain are available in public databases, making it difficult to address the emergence of recombinant EVs, understand their evolutionary relatedness and the possible implication in human disease. We have used metagenomic (untargeted) NGS to generate full-length EV genomes from CSF samples of EV-positive aseptic meningitis cases in Southern Spain between 2015 and 2018. Our analyses reveal the co-circulation of multiple Enterovirus B (EV-B) types (E6, E11, E13 and E30), including a novel E13 recombinant form. We observed a genetic turnover where emergent lineages (C1 for E6 and I [tentatively proposed in this study] for E30) replaced previous lineages circulating in Spain, some concomitant with outbreaks in other parts of Europe. Metagenomic sequencing provides an effective approach for the analysis of EV genomes directly from PCR-positive CSF samples. The detection of a novel, disease-associated, recombinant form emphasizes the importance of genomic surveillance to monitor spread and evolution of EVs.

European Non-Polio Enterovirus Network: Introduction of Hospital-Based Surveillance Network to Understand the True Disease Burden of Non-Polio Enterovirus and Parechovirus Infections in Europe

BACKGROUND

Non-polio enteroviruses (EVs) and human parechoviruses (PeVs) cause a wide range of human infections. Limited data on their true disease burden exist as standardized European-wide surveillance is lacking.

AIMS

Our aim is to estimate the disease burden of EV and PeV infections in Europe via establishment of standardized surveillance for hand, foot and mouth disease (HFMD) and respiratory and neurological infections caused by these viruses. We will also assess the sensitivity of assays implemented in the network of participating laboratories so that all EV and PeV types are adequately detected. Plan. The European Non-Polio Enterovirus Network (ENPEN) has developed standardized protocols for a prospective, multi-center and cross-sectional hospital-based pilot study. Protocols include guidance for diagnosis, case definition, detection, characterization and reporting of EV and PeV infections associated with HFMD and respiratory and neurological diseases. Over 30 sites from 17 European countries have already registered to this one pilot study, likely to be commenced in 2022.

BENEFITS

This surveillance will allow European-wide comparison of data on EV and PeV infection. These data will also be used to determine the burden of EV and PeV infections, which is needed to guide the further prevention measures and policies.

Molecular Epidemiology and Evolutionary Trajectory of Emerging Echovirus 30, Europe

In 2018, an upsurge in echovirus 30 (E30) infections was reported in Europe. We conducted a large-scale epidemiologic and evolutionary study of 1,329 E30 strains collected in 22 countries in Europe during 2016-2018. Most E30 cases affected persons 0-4 years of age (29%) and 25-34 years of age (27%). Sequences were divided into 6 genetic clades (G1-G6). Most (53%) sequences belonged to G1, followed by G6 (23%), G2 (17%), G4 (4%), G3 (0.3%), and G5 (0.2%). Each clade encompassed unique individual recombinant forms; G1 and G4 displayed >2 unique recombinant forms. Rapid turnover of new clades and recombinant forms occurred over time. Clades G1 and G6 dominated in 2018, suggesting the E30 upsurge was caused by emergence of 2 distinct clades circulating in Europe. Investigation into the mechanisms behind the rapid turnover of E30 is crucial for clarifying the epidemiology and evolution of these enterovirus infections.

Temporal phylogeny and molecular characterization of echovirus 30 associated with aseptic meningitis outbreaks in China

BACKGROUND

An outbreak of aseptic meningitis occurred from June to August 2016, in Inner Mongolia Autonomous Region, China.

METHODS

To determine its epidemiological characteristics, etiologic agent, and possible origin, specimens were collected for virus isolation and identification, followed by molecular epidemiological analysis.

RESULTS

A total of 363 patients were clinically diagnosed from June 1st to August 31st 2016, and most cases (63.1%, n = 229) were identified between June 22nd and July 17th, with children aged 6 to 12 years constituting the highest percentage (68.9%, n = 250). All viral isolates from this study belonged to genotype C of echovirus 30 (E30), which dominated transmission in China. To date, two E30 transmission lineages have been identified in China, of which Lineage 2 was predominant. We observed fluctuant progress of E30 genetic diversity, with Lineage 2 contributing to increased genetic diversity after 2002, whereas Lineage 1 was significant for the genetic diversity of E30 before 2002.

CONCLUSIONS

We identified the epidemiological and etiological causes of an aseptic meningitis outbreak in Inner Mongolia in 2016, and found that Lineage 2 played an important role in recent outbreaks. Moreover, we found that Gansu province could play an important role in E30 spread and might be a possible origin site. Furthermore, Fujian, Shandong, Taiwan, and Zhejiang provinces also demonstrated significant involvement in E30 evolution and persistence over time in China.

Genetic diversity and evolution of enterovirus A71 subgenogroup C1 from children with hand, foot, and mouth disease in Thailand

Enterovirus A71 (EV-A71) can cause hand, foot, and mouth disease (HFMD) in children and may be associated with severe neurological complications. There have been numerous reports of increased incidence of EV-A71 subgenogroup C1 (EV-A71 C1) infections associated with neurological diseases since the first occurrence in Germany in 2015. Here, we describe 11 full-length genome sequences of 2019 EV-A71 C1 strains isolated from HFMD patients in Thailand from 2019 to early 2020. The genetic evolution of 2019 EV-A71 C1 was traced in the outbreaks, and the emergence of multiple lineages was detected. Our results demonstrated that 2019 EV-A71 C1 from Thailand emerged through recombination between its nonstructural protein gene and those of other EV-A genotypes. Bayesian-based phylogenetic analysis showed that the 2019 EV-A71 C1 Thai strains share a common ancestor with variants in Europe (Denmark and France). The substitution rate for the 2019 EV-A71 C1 genome was estimated to be 4.38 × 10^-3 substitutions/(site∙year^-1) (95% highest posterior density interval: 3.84-4.94 × 10^-3 substitutions/[site∙year^-1]), approximating that observed between previous EV-A71 C1 outbreaks. These data are essential for understanding the evolution of EV-A C1 during the ongoing HFMD outbreak and may be relevant to disease outcomes in children worldwide.

Epidemiology and Sequence-Based Evolutionary Analysis of Circulating Non-Polio Enteroviruses

Enteroviruses (EVs) are positive-sense RNA viruses, with over 50,000 nucleotide sequences publicly available. While most human infections are typically associated with mild respiratory symptoms, several different EV types have also been associated with severe human disease, especially acute flaccid paralysis (AFP), particularly with endemic members of the EV-B species and two pandemic types—EV-A71 and EV-D68—that appear to be responsible for recent widespread outbreaks. Here we review the recent literature on the prevalence, characteristics, and circulation dynamics of different enterovirus types and combine this with an analysis of the sequence coverage of different EV types in public databases (e.g., the Virus Pathogen Resource). This evaluation reveals temporal and geographic differences in EV circulation and sequence distribution, highlighting recent EV outbreaks and revealing gaps in sequence coverage. Phylogenetic analysis of the EV genus shows the relatedness of different EV types. Recombination analysis of the EV-A species provides evidence for recombination as a mechanism of genomic diversification. The absence of broadly protective vaccines and effective antivirals makes human enteroviruses important pathogens of public health concern.

Structures of Echovirus 30 in complex with its receptors inform a rational prediction for enterovirus receptor usage

Receptor usage that determines cell tropism and drives viral classification closely correlates with the virus structure. Enterovirus B (EV-B) consists of several subgroups according to receptor usage, among which echovirus 30 (E30), a leading causative agent for human aseptic meningitis, utilizes FcRn as an uncoating receptor. However, receptors for many EVs remain unknown. Here we analyzed the atomic structures of E30 mature virion, empty- and A-particles, which reveals serotype-specific epitopes and striking conformational differences between the subgroups within EV-Bs. Of these, the VP1 BC loop markedly distinguishes E30 from other EV-Bs, indicative of a role as a structural marker for EV-B. By obtaining cryo-electron microscopy structures of E30 in complex with its receptor FcRn and CD55 and comparing its homologs, we deciphered the underlying molecular basis for receptor recognition. Together with experimentally derived viral receptor identifications, we developed a structure-based in silico algorithm to inform a rational prediction for EV receptor usage.

Echovirus 30 (E30) belongs to the Enterovirus-B group and causes aseptic meningitis in humans. Here, the authors present the cryo-EM structures of the E30 E-particle, A-particle and the mature virion, as well as structures of E30 in complex with its receptor FcRn and CD55, and furthermore they describe a structure-based algorithm that allows the prediction of EV receptor usage.

Serotype specific epitopes identified by neutralizing antibodies underpin immunogenic differences in Enterovirus B

Echovirus 30 (E30), a serotype of Enterovirus B (EV-B), recently emerged as a major causative agent of aseptic meningitis worldwide. E30 is particularly devastating in the neonatal population and currently no vaccine or antiviral therapy is available. Here we characterize two highly potent E30-specific monoclonal antibodies, 6C5 and 4B10, which efficiently block binding of the virus to its attachment receptor CD55 and uncoating receptor FcRn. Combinations of 6C5 and 4B10 augment the sum of their individual anti-viral activities. High-resolution structures of E30-6C5-Fab and E30-4B10-Fab define the location and nature of epitopes targeted by the antibodies. 6C5 and 4B10 engage the capsid loci at the north rim of the canyon and in-canyon, respectively. Notably, these regions exhibit antigenic variability across EV-Bs, highlighting challenges in development of broad-spectrum antibodies. Our structures of these neutralizing antibodies of E30 are instructive for development of vaccines and therapeutics against EV-B infections.

So far no vaccine or antiviral therapy is available for Echovirus 30 (E30) that causes aseptic meningitis. Here, the authors generate and characterise two E30-specific monoclonal antibodies that block binding of the virus to its attachment receptor CD55 and uncoating receptor FcRn, and determine the cryo-EM structures of E30 with the bound neutralizing antibodies.

An Extended Primer Grip of Picornavirus Polymerase Facilitates Sexual RNA Replication Mechanisms

Picornaviruses have both asexual and sexual RNA replication mechanisms. Asexual RNA replication mechanisms involve one parental template, whereas sexual RNA replication mechanisms involve two or more parental templates. Because sexual RNA replication mechanisms counteract ribavirin-induced error catastrophe, we selected for ribavirin-resistant poliovirus to identify polymerase residues that facilitate sexual RNA replication mechanisms. We used serial passage in ribavirin, beginning with a variety of ribavirin-sensitive and ribavirin-resistant parental viruses. Ribavirin-sensitive virus contained an L420A polymerase mutation, while ribavirin-resistant virus contained a G64S polymerase mutation. A G64 codon mutation (G64Fix) was used to inhibit emergence of G64S-mediated ribavirin resistance. Revertants (L420) or pseudorevertants (L420V and L420I) were selected from all independent lineages of L420A, G64Fix L420A, and G64S L420A parental viruses. Ribavirin resistance G64S mutations were selected in two independent lineages, and novel ribavirin resistance mutations were selected in the polymerase in other lineages (M299I, M323I, M392V, and T353I). The structural orientation of M392, immediately adjacent to L420 and the polymerase primer grip region, led us to engineer additional polymerase mutations into poliovirus (M392A, M392L, M392V, K375R, and R376K). L420A revertants and pseudorevertants (L420V and L420I) restored efficient viral RNA recombination, confirming that ribavirin-induced error catastrophe coincides with defects in sexual RNA replication mechanisms. Viruses containing M392 mutations (M392A, M392L, and M392V) and primer grip mutations (K375R and R376K) exhibited divergent RNA recombination, ribavirin sensitivity, and biochemical phenotypes, consistent with changes in the fidelity of RNA synthesis. We conclude that an extended primer grip of the polymerase, including L420, M392, K375, and R376, contributes to the fidelity of RNA synthesis and to efficient sexual RNA replication mechanisms.IMPORTANCE Picornaviruses have both asexual and sexual RNA replication mechanisms. Sexual RNA replication shapes picornavirus species groups, contributes to the emergence of vaccine-derived polioviruses, and counteracts error catastrophe. Can viruses distinguish between homologous and nonhomologous partners during sexual RNA replication? We implicate an extended primer grip of the viral polymerase in sexual RNA replication mechanisms. By sensing RNA sequence complementarity near the active site, the extended primer grip of the polymerase has the potential to distinguish between homologous and nonhomologous RNA templates during sexual RNA replication.

Molecular epidemiology of enteroviruses associated with severe hand, foot and mouth disease in Shenzhen, China, 2014-2018

In this study, we investigated the epidemiology and molecular characteristics of enteroviruses associated with severe hand, foot and mouth disease (HFMD) in Shenzhen, China, during 2014-2018. A total of 137 fecal specimens from patients with severe HFMD were collected. Enterovirus (EV) types were determined using real-time reverse transcription polymerase chain reaction (RT-PCR), RT nested PCR, and sequencing. Sequences were analyzed using bioinformatics programs. Of 137 specimens tested, 97 (70.8%), 12 (8.8%), and 10 (7.3%) were positive for EV-A71, coxsackievirus A6 (CVA6), and CVA16, respectively. Other pathogens detected included CVA2 (2.9%, 4/137), CVA10 (2.9%, 4/137), CVA5 (0.7%, 1/137), echovirus 6 (E6) (0.7%, 1/137) and E18 (0.7%, 1/137). The most frequent complication in patients with proven EV infections was myoclonic jerk, followed by aseptic encephalitis, tachypnea, and vomiting. The frequencies of vomiting and abnormal eye movements were higher in EV-A71-infected patients than that in CVA6-infected or CVA16-infected patients. Molecular phylogeny based on the complete VP1 gene revealed no association between the subgenotype of the virus and disease severity. Nevertheless, 12 significant mutations that were likely to be associated with virulence or the clinical phenotype were observed in the 5’UTR, 2A^pro, 2C, 3A, 3D^pol and 3’UTR of CVA6. Eight significant mutations were observed in the 5’UTR, 2B, 3A, 3D^pol and 3’UTR of CVA16, and 10 significant mutations were observed in the 5’UTR, VP1, 3A and 3C^pro of CVA10. In conclusion, EV-A71 is still the main pathogen causing severe HFMD, although other EV types can also cause severe complications. Potential virulence or phenotype-associated sites were identified in the genomes of CVA6, CVA16, and CVA10.

Genetic recombination in fast-spreading coxsackievirus A6 variants: a potential role in evolution and pathogenicity

Hand, foot, and mouth disease (HFMD) is a common global epidemic. From 2008 onwards, many HFMD outbreaks caused by coxsackievirus A6 (CV-A6) have been reported worldwide. Since 2013, with a dramatically increasing number of CV-A6-related HFMD cases, CV-A6 has become the predominant HFMD pathogen in mainland China. Phylogenetic analysis based on the VP1 capsid gene revealed that subtype D3 dominated the CV-A6 outbreaks. Here, we performed a large-scale (near) full-length genetic analysis of global and Chinese CV-A6 variants, including 158 newly sequenced samples collected extensively in mainland China between 2010 and 2018. During the global transmission of subtype D3 of CV-A6, the noncapsid gene continued recombining, giving rise to a series of viable recombinant hybrids designated evolutionary lineages, and each lineage displayed internal consistency in both genetic and epidemiological features. The emergence of lineage –A since 2005 has triggered CV-A6 outbreaks worldwide, with a rate of evolution estimated at 4.17 × 10⁻³ substitutions site^-1 year⁻¹ based on a large number of monophyletic open reading frame sequences, and created a series of lineages chronologically through varied noncapsid recombination events. In mainland China, lineage –A has generated another two novel widespread lineages (–J and –L) through recombination within the enterovirus A gene pool, with robust estimates of occurrence time. Lineage –A, –J, and –L infections presented dissimilar clinical manifestations, indicating that the conservation of the CV-A6 capsid gene resulted in high transmissibility, but the lineage-specific noncapsid gene might influence pathogenicity. Potentially important amino acid substitutions were further predicted among CV-A6 variants. The evolutionary phenomenon of noncapsid polymorphism within the same subtype observed in CV-A6 was uncommon in other leading HFMD pathogens; such frequent recombination happened in fast-spreading CV-A6, indicating that the recovery of deleterious genomes may still be ongoing within CV-A6 quasispecies. CV-A6-related HFMD outbreaks have caused a significant public health burden and pose a great threat to children’s health; therefore, further surveillance is greatly needed to understand the full genetic diversity of CV-A6 in mainland China.

Recombination Analysis of Non-Poliovirus Members of the Enterovirus C Species; Restriction of Recombination Events to Members of the Same 3DPol Cluster

Enteroviruses (EVs) are highly prevalent viruses worldwide. Recombination is known to occur frequently in EVs belonging to species Enterovirus A, Enterovirus B, and Enterovirus C. Although many recombinant vaccine-derived poliovirus (VDPV) strains have been reported, our knowledge on recombination in non-polio EVs in the species Enterovirus C is limited. Here, we combined a dataset consisting of 11 newly generated full-length Enterovirus C sequences and 180 publicly available sequences to study recombination dynamics in non-polio EVs. To identify recombination patterns, maximum likelihood phylogenetic trees of different genomic regions were constructed, and segregation analyses were performed. Recombination was observed between members of the same 3DPol cluster, but was rarely observed between members of different clusters. We hypothesize that this restriction may have arisen through their different compartmentalization in respiratory and enteric tracts related to differences in cellular tropisms so that the opportunity to recombine may not be available.

Circulation of non-polio enteroviruses in 24 EU and EEA countries between 2015 and 2017: a retrospective surveillance study

BACKGROUND

Enteroviruses can cause severe infections, especially in young children. Non-polio enterovirus infections are not notifiable in most countries in the EU and European Economic Area (EEA) region, and surveillance varies substantially between countries. We collected and analysed available enterovirus data across EU and EEA countries to assess the current epidemiological situation and need for standardising surveillance.

METHODS

Aggregated data on any enterovirus detected between Jan 1, 2015, and Dec 31, 2017, through national enterovirus reference laboratories were requested from representatives in all 31 EU and EEA countries. Information collected included enterovirus types detected by month, patient age group, symptom, and specimen type. We also collected sequence data on viral capsid sequences for the three most clinically relevant enterovirus types, as identified from the data.

FINDINGS

Aggregated data were provided by representatives from 24 (77%) of 31 countries. 9914 (66%) of 14 999 enterovirus infections with information about age were in children younger than 5 years, and 3197 (45%) of 7139 individuals for whom symptoms were reported had neurological symptoms. Other symptoms were non-specific fever (in 1607 [23%] patients), respiratory symptoms (in 1197 [17%] patients), hand, foot, and mouth disease (in 528 [7% patients), and myocarditis (in 39 [1%] patients). 68 deaths were temporally associated with enterovirus infection. Typing for 11 559 (67%) of 17 136 specimens revealed 66 enterovirus types. Coxsackievirus A6 was the most frequently detected enterovirus type (in 1556 [13%] of 11 559 typed enteroviruses), and 292 (65%) of 448 patients with coxsackievirus A6 infection with available clinical data presented with hand, foot, and mouth disease. Echovirus 30 was the second most frequently detected enterovirus type, representing 1412 (12%) of 11 559 typed enteroviruses, and 384 (82%) of 467 individuals with echovirus 30 infection with available clinical data had neurological symptoms. Sequences available from 18 countries showed circulation of newly emerging strains of enterovirus A71 and enterovirus D68.

INTERPRETATION

To our knowledge, this study is the largest investigation of enterovirus circulation in EU and EEA countries and confirms the availability of non-polio enterovirus data in the region. Our study highlights the wide circulation of non-polio enteroviruses in Europe, mostly affecting young children and leading to neurological symptoms. Collecting data on morbidity and mortality related to enterovirus infections, as well as harmonising case definition for surveillance, should be encouraged.

FUNDING

None.

Evolutionary and Structural Overview of Human Picornavirus Capsid Antibody Evasion

Picornaviruses constitute one of the most relevant viral groups according to their impact on human and animal health. Etiologic agents of a broad spectrum of illnesses with a clinical presentation that ranges from asymptomatic to fatal disease, they have been the cause of uncountable epidemics throughout history. Picornaviruses are small naked RNA-positive single-stranded viruses that include some of the most important pillars in the development of virology, comprising poliovirus, rhinovirus, and hepatitis A virus. Picornavirus infectious particles use the fecal-oral or respiratory routes as primary modes of transmission. In this regard, successful viral spread relies on the capability of viral capsids to (i) shelter the viral genome, (ii) display molecular determinants for cell receptor recognition, (iii) facilitate efficient genome delivery, and (iv) escape from the immune system. Importantly, picornaviruses display a substantial amount of genetic variability driven by both mutation and recombination. Therefore, the outcome of their replication results in the emergence of a genetically diverse cloud of individuals presenting phenotypic variance. The host humoral response against the capsid protein represents the most active immune pressure and primary weapon to control the infection. Since the preservation of the capsid function is deeply rooted in the virus evolutionary dynamics, here we review the current structural evidence focused on capsid antibody evasion mechanisms from that perspective.

Genomic analysis of serologically untypable human enteroviruses in Taiwan

BACKGROUND

Human enteroviruses contain over 100 serotypes. We have routinely conducted enterovirus surveillance in northern Taiwan; but about 10% of isolates could not be serotyped using traditional assays. Next-generation sequencing (NGS) is a powerful tool for genome sequencing.

METHODS

In this study, we established an NGS platform to conduct genome sequencing for the serologically untypable enterovirus isolates.

RESULTS

Among 130 serologically untypable isolates, 121 (93%) of them were classified into 29 serotypes using CODEHOP (COnsensus-DEgenerate Hybrid Oligonucleotide Primer)-based RT-PCR to amplify VP1 genes (VP1-CODEHOP). We further selected 52 samples for NGS and identified 59 genome sequences from 51 samples, including 8 samples containing two virus genomes. We also detected 23 genome variants (nucleotide identity < 90% compared with genome sequences in the public domain) which were potential genetic recombination, including 9 inter-serotype recombinants and 14 strains with unknown sources of recombination.

CONCLUSIONS

We successfully integrated VP1-CODEHOP and NGS techniques to conduct genomic analysis of serologically untypable enteroviruses.

Predicting Intraserotypic Recombination in Enterovirus 71

Enteroviruses are well known for their ability to cause neurological damage and paralysis. The model enterovirus is poliovirus (PV), the causative agent of poliomyelitis, a condition characterized by acute flaccid paralysis. A related virus, enterovirus 71 (EV-A71), causes similar clinical outcomes in recurrent outbreaks throughout Asia. Retrospective phylogenetic analysis has shown that recombination between circulating strains of EV-A71 produces the outbreak-associated strains which exhibit increased virulence and/or transmissibility. While studies on the mechanism(s) of recombination in PV are ongoing in several laboratories, little is known about factors that influence recombination in EV-A71. We have developed a cell-based assay to study recombination of EV-A71 based upon previously reported assays for poliovirus recombination. Our results show that (i) EV-A71 strain type and RNA sequence diversity impacts recombination frequency in a predictable manner that mimics the observations found in nature; (ii) recombination is primarily a replicative process mediated by the RNA-dependent RNA polymerase; (iii) a mutation shown to reduce recombination in PV (L420A) similarly reduces EV-A71 recombination, suggesting conservation in mechanism(s); and (iv) sequencing of intraserotypic recombinant genomes indicates that template switching occurs by a mechanism that may require some sequence homology at the recombination junction and that the triggers for template switching may be sequence independent. The development of this recombination assay will permit further investigation on the interplay between replication, recombination and disease.IMPORTANCE Recombination is a mechanism that contributes to genetic diversity. We describe the first assay to study EV-A71 recombination. Results from this assay mimic what is observed in nature and can be used by others to predict future recombination events within the enterovirus species A group. In addition, our results highlight the central role played by the viral RNA-dependent RNA polymerase (RdRp) in the recombination process. Further, our results show that changes to a conserved residue in the RdRp from different species groups have a similar impact on viable recombinant virus yields, which is indicative of conservation in mechanism.

Evolutionary Virology at 40

RNA viruses are diverse, abundant, and rapidly evolving. Genetic data have been generated from virus populations since the late 1970s and used to understand their evolution, emergence, and spread, culminating in the generation and analysis of many thousands of viral genome sequences. Despite this wealth of data, evolutionary genetics has played a surprisingly small role in our understanding of virus evolution. Instead, studies of RNA virus evolution have been dominated by two very different perspectives, the experimental and the comparative, that have largely been conducted independently and sometimes antagonistically. Here, we review the insights that these two approaches have provided over the last 40 years. We show that experimental approaches using in vitro and in vivo laboratory models are largely focused on short-term intrahost evolutionary mechanisms, and may not always be relevant to natural systems. In contrast, the comparative approach relies on the phylogenetic analysis of natural virus populations, usually considering data collected over multiple cycles of virus-host transmission, but is divorced from the causative evolutionary processes. To truly understand RNA virus evolution it is necessary to meld experimental and comparative approaches within a single evolutionary genetic framework, and to link viral evolution at the intrahost scale with that which occurs over both epidemiological and geological timescales. We suggest that the impetus for this new synthesis may come from methodological advances in next-generation sequencing and metagenomics.

Mechanisms and consequences of positive-strand RNA virus recombination

Genetic recombination in positive-strand RNA viruses is a significant evolutionary mechanism that drives the creation of viral diversity by the formation of novel chimaeric genomes. The process and its consequences, for example the generation of viruses with novel phenotypes, has historically been studied by analysis of the end products. More recently, with an appreciation that there are both replicative and non-replicative mechanisms at work, and with new approaches and techniques to analyse intermediate products, the viral and cellular factors that influence the process are becoming understood. The major influence on replicative recombination is the fidelity of viral polymerase, although RNA structures and sequences may also have an impact. In replicative recombination the viral polymerase is necessary and sufficient, although roles for other viral or cellular proteins may exist. In contrast, non-replicative recombination appears to be mediated solely by cellular components. Despite these insights, the relative importance of replicative and non-replicative mechanisms is not clear. Using single-stranded positive-sense RNA viruses as exemplars, we review the current state of understanding of the processes and consequences of recombination.

Serotype-specific immunity explains the incidence of diseases caused by human enteroviruses

Human enteroviruses are a major cause of neurological and other diseases. More than 100 serotypes are known that exhibit unexplained complex patterns of incidence, from regular cycles to more irregular patterns, and new emergences. Using 15 years of surveillance data from Japan (2000-2014) and a stochastic transmission model with accurate demography, we show that acquired serotype-specific immunity can explain the diverse patterns of 18 of the 20 most common serotypes (including Coxsackieviruses, Echoviruses, and Enterovirus-A71). The remaining two serotypes required a change in viral characteristics, including an increase in pathogenicity for Coxsackievirus-A6, which is consistent with its recent global rise in incidence. On the basis of our findings, we are able to predict outbreaks 2 years ahead of time (2015-2016). These results have implications for the impact of vaccines under development.

Molecular epidemiology and phylogenetics of human enteroviruses: Is there a forest behind the trees?

Enteroviruses are among the best studied small non-enveloped enteric RNA viruses. Most enteroviruses are easy to isolate in cell culture, and many non-polio enterovirus strains were archived worldwide as a byproduct of the WHO poliovirus surveillance system. Common outbreaks and epidemics, most prominently the epidemic of hand-foot-and-mouth disease with severe neurological complications in East and South-East Asia, justify practical interest of non-polio enteroviruses. As a result, there are over 50 000 enterovirus nucleotide sequences available in GenBank. Technical possibilities have been also improving, as Bayesian phylogenetic methods with an integrated molecular clock were introduced a decade ago and provided unprecedented opportunities for phylogenetic analysis. As a result, hundreds of papers were published on the molecular epidemiology of enteroviruses. This review covers the modern methodology, structure, and biases of the sequence dataset available in GenBank. The relevance of the subtype classification, findings of co-circulation of multiple genetic variants, previously unappreciated complexity of viral populations, and global evolutionary patterns are addressed. The most relevant conclusions and prospects for further studies on outbreak emergence mechanisms are discussed.

Evolution of echovirus 11 in a chronically infected immunodeficient patient

Deep sequencing was used to determine complete nucleotide sequences of echovirus 11 (EV11) strains isolated from a chronically infected patient with CVID as well as from cases of acute enterovirus infection. Phylogenetic analysis showed that EV11 strains that circulated in Israel in 1980-90s could be divided into four clades. EV11 strains isolated from a chronically infected individual belonged to one of the four clades and over a period of 4 years accumulated mutations at a relatively constant rate. Extrapolation of mutations accumulation curve into the past suggested that the individual was infected with circulating EV11 in the first half of 1990s. Genomic regions coding for individual viral proteins did not appear to be under strong selective pressure except for protease 3C that was remarkably conserved. This may suggest its important role in maintaining persistent infection.

We describe evolution of Echovirus 11 genome in chronically infected immunodeficient patient over a period of several years and compare it with the evolution of circulating echoviruses from which it originated. Ratio of silent to missense mutations in protein coding regions suggests that chronic virus was under lower selective pressure than circulating viruses, except for a region coding for viral protease that may participate in neutralizing host cell anti-viral defense mechanisms. This suggests that adaptation to persistence in immunodeficient host may require maintaining functional viral counter-defense mechanisms.

Environmental Surveillance of Enteroviruses in Central Argentina: First Detection and Evolutionary Analyses of E14

Environmental surveillance is an effective approach to investigate the circulation of human enteroviruses in the population. Enteroviruses E14, CVA9, E-6, E16, E20, E25, E13, and CVA24 were detected in sewage and a watercourse in central Argentina. E14 was the most frequent serotype and was found for the first time in environmental samples in our region. Phylogenetic and coalescence analyses showed at least two recent introduction events.

Recombination in the rabies virus and other lyssaviruses

Recombination is a common event in RNA viruses; however, in the rabies virus there have been only a few reports of isolated recombination events. Comprehensive analysis found traces of recent recombination events within Arctic, Arctic-like and Africa 1b rabies virus groups, as well as recombination between distinct lyssaviruses. Recombination breakpoints were not linked to gene boundaries and could be detected all over the genome. However, there was no evidence that recombination is an important factor in the genetic variability of the rabies virus. It is therefore likely that recombination in the rabies virus is limited by ecological factors (e.g., rare co-circulation of distinguishable lineages and a narrow window for productive coinfection in most carnivore hosts), rather than molecular barriers (e.g., incompatibility of genome fragments).

Molecular evolution of types in non-polio enteroviruses

Non-polio enteroviruses are a ubiquitous and divergent group of non-enveloped RNA viruses. Novel types are reported regularly in addition to over 100 known types; however, mechanisms of emergence of novel types remain obscure. Here, the 33 most common types represented by 35-629 non-redundant partial VP1 sequences in GenBank were studied in parallel using Bayesian coalescent molecular clock analysis to investigate common evolutionary trends among enterovirus types. Inferred substitution rates were in the range of 0.41×10^-2 to 3.07×10^-2 substitutions per site per year. The most recent common ancestors of known isolates of each type presumably existed between 55 and 200 years ago. Phylogenetic analysis results suggested that global type populations underwent bottlenecks that could repeatedly reset the common ancestor dates. Nevertheless, species-level analysis suggested that the contemporary enterovirus types emerged within the last millennium. Analysis of 2657 complete VP1 sequences of the 24 most common types indicated that the type criterion based upon 75 % nucleotide sequence identity remains generally valid, despite exponential growth of the number of known sequences and a high rate of mutation fixation. However, in few types there was evidence that enteroviruses can drift slightly beyond the type threshold, up to 73 % identity, and both amino acid and nucleotide sequences should be considered for type identification. Analysis of sequence distances within types implied that sequence-identity-based identification of genotypes is rational within some, but not all, types and distinct genotype cut-offs (9-20 %) may be useful for different types.

VIRO-TypeNed, systematic molecular surveillance of enteroviruses in the Netherlands between 2010 and 2014

VIRO-TypeNed is a collaborative molecular surveillance platform facilitated through a web-based database. Genetic data in combination with epidemiological, clinical and patient data are shared between clinical and public health laboratories, as part of the surveillance underpinning poliovirus eradication. We analysed the combination of data submitted from 2010 to 2014 to understand circulation patterns of non-polio enteroviruses (NPEV) of public health relevance. Two epidemiological patterns were observed based on VIRO-TypeNed data and classical surveillance data dating back to 1996: (i) endemic cyclic, characterised by predictable upsurges/outbreaks every two to four years, and (ii) epidemic, where rare virus types caused upsurges/outbreaks. Genetic analysis suggests continuous temporal displacement of virus lineages due to the accumulation of (silent) genetic changes. Non-synonymous changes in the antigenic B/C loop suggest antigenic diversification, which may affect population susceptibility. Infections were frequently detected at an age under three months and at an older, parenting age (25–49 years) pointing to a distinct role of immunity in the circulation patterns. Upsurges were detected in the summer and winter which can promote increased transmissibility underlying new (cyclic) upsurges and requires close monitoring. The combination of data provide a better understanding of NPEV circulation required to control and curtail upsurges and outbreaks.

African Non-Human Primates Host Diverse Enteroviruses

Enteroviruses (EVs) belong to the family Picornaviridae and are responsible for mild to severe diseases in mammals including humans and non-human primates (NHP). Simian EVs were first discovered in the 1950s in the Old World Monkeys and recently in wild chimpanzee, gorilla and mandrill in Cameroon. In the present study, we screened by PCR EVs in 600 fecal samples of wild apes and monkeys that were collected at four sites in Gabon. A total of 32 samples were positive for EVs (25 from mandrills, 7 from chimpanzees, none from gorillas). The phylogenetic analysis of VP1 and VP2 genes showed that EVs identified in chimpanzees were members of two human EV species, EV-A and EV-B, and those identified in mandrills were members of the human species EV-B and the simian species EV-J. The identification of two novel enterovirus types, EV-B112 in a chimpanzee and EV-B113 in a mandrill, suggests these NHPs could be potential sources of new EV types. The identification of EV-B107 and EV90 that were previously found in humans indicates cross-species transfers. Also the identification of chimpanzee-derived EV110 in a mandrill demonstrated a wide host range of this EV. Further research of EVs in NHPs would help understanding emergence of new types or variants, and evaluating the real risk of cross-species transmission for humans as well for NHPs populations.

Intertypic recombination of human parechovirus 4 isolated from infants with sepsis-like disease

BACKGROUND

Human parechoviruses (HPeVs) (family Picornaviridae), are common pathogens in young children. Despite their high prevalence, research on their genetic identity, diversity and evolution have remained scarce.

OBJECTIVES

Complete coding regions of three previously reported HPeV-4 isolates from Finnish children with sepsis-like disease were sequenced in order to elucidate the phylogenetic relationships and potential recombination events during the evolution of these isolates.

STUDY DESIGN

The isolated viruses were sequenced and aligned with all HPeV complete genome sequences available in GenBank. Phylogenetic trees were constructed and similarity plot and bootscanning methods were used for recombination analysis.

RESULTS

The three HPeV-4 isolates had 99.8% nucleotide sequence similarity. The phylogenetic analysis indicated that capsid-encoding sequences of these HPeV-4 isolates were closely related to other HPeV-4 strains (80.7-94.7% nucleotide similarity), whereas their non-structural region genes 2A to 3C clustered together with several HPeV-1 and HPeV-3 strains, in addition to the HPeV-4 strain K251176-02 (isolated 2002 in the Netherlands), but not with other HPeV-4 strains. However, in 3D-encoding sequence the Finnish HPeV-4 isolates did not cluster with the strain HPeV-4/K251176-02, but instead, formed a distinct group together with several HPeV-1 and HPeV-3 strains. Similarity plot and Bootscan analyses further confirmed intertypic recombination events in the evolution of the Finnish HPeV-4 isolates.

CONCLUSION

Intertypic recombination event(s) have occurred during the evolution of HPeV-4 isolates from children with sepsis-like disease. However, due to the low number of parechovirus complete genomes available, the precise recombination partners could not be detected. The results suggest frequent intratypic recombination among parechoviruses.

Analysis of an echovirus 18 outbreak in Thuringia, Germany: insights into the molecular epidemiology and evolution of several enterovirus species B members

In October and November 2010, six children and one woman were presented with symptoms of aseptic meningitis in Jena, Thuringia, Germany. Enterovirus RNA was detected in the cerebrospinal fluid of all patients by RT-PCR, and preliminary molecular typing revealed echovirus 18 (E-18) as causative agent. Virus isolates were obtained from stool samples of three patients and several contact persons. Again, most isolates were typed as E-18. In addition, coxsackievirus B5 (CV-B5) and echovirus 25 (E-25) were found to co-circulate. As only few complete E-18 sequences are available in GenBank, the entire genomes of these isolates were determined using direct RNA-sequencing technology. We did not find evidence for recombination between E-18, E-25 or CV-B5 during the outbreak. Viral protein 1 gene sequences and the cognate 3D polymerase gene sequences of each isolate and GenBank sequences were analysed in order to define type-specific recombination groups (recogroups).

Biochemical and genetic analysis of the role of the viral polymerase in enterovirus recombination

Genetic recombination in single-strand, positive-sense RNA viruses is a poorly understand mechanism responsible for generating extensive genetic change and novel phenotypes. By moving a critical cis-acting replication element (CRE) from the polyprotein coding region to the 3′ non-coding region we have further developed a cell-based assay (the 3′CRE-REP assay) to yield recombinants throughout the non-structural coding region of poliovirus from dually transfected cells. We have additionally developed a defined biochemical assay in which the only protein present is the poliovirus RNA dependent RNA polymerase (RdRp), which recapitulates the strand transfer events of the recombination process. We have used both assays to investigate the role of the polymerase fidelity and nucleotide turnover rates in recombination. Our results, of both poliovirus intertypic and intratypic recombination in the CRE-REP assay and using a range of polymerase variants in the biochemical assay, demonstrate that RdRp fidelity is a fundamental determinant of recombination frequency. High fidelity polymerases exhibit reduced recombination and low fidelity polymerases exhibit increased recombination in both assays. These studies provide the basis for the analysis of poliovirus recombination throughout the non-structural region of the virus genome and provide a defined biochemical assay to further dissect this important evolutionary process.

The epidemiology of non-polio enteroviruses: recent advances and outstanding questions

PURPOSE OF REVIEW

There are over 100 serotypes of human enteroviruses, which cause a spectrum of illnesses, including meningitis, encephalitis, paralysis, myocarditis and rash. Increasing incidence of hand-foot-and-mouth disease in the Asia-Pacific region and recent outbreaks of enterovirus-associated disease, such as severe respiratory illness in the United States in 2014, highlight the threat of these viruses to human health.

RECENT FINDINGS

We describe recent outbreaks of human enteroviruses and summarize knowledge gaps regarding their burden, spectrum of diseases and epidemiology.

SUMMARY

Reported outbreaks of respiratory, neurological, skin and eye diseases associated with human enteroviruses have increased in frequency and size in recent years. Improved molecular diagnostics and genetic sequence analysis are beginning to reveal the complex dynamics of individual serotypes and genotypes, and their contribution to these outbreaks. However, the biological mechanisms underlying their emergence and transmission dynamics remain elusive. They are likely to involve changes in the virus, such as fitness, antigenicity, virulence or tropism, and in the human population, such as levels of sanitation and of homotypic and heterotypic immunity. Improvements in surveillance, serological surveys and detailed genetic and antigenic characterization of viral populations would help to elucidate these mechanisms. This will be important for the design of outbreak control and vaccine development strategies.

Enterovirus Migration Patterns between France and Tunisia

The enterovirus (EV) types echovirus (E-) 5, E-9, and E-18, and coxsackievirus (CV-) A9 are infrequently reported in human diseases and their epidemiologic features are poorly defined. Virus transmission patterns between countries have been estimated with phylogenetic data derived from the 1D/VP1 and 3CD gene sequences of a sample of 74 strains obtained in France (2000–2012) and Tunisia (2011–2013) and from the publicly available sequences. The EV types (E-5, E-9, and E-18) exhibited a lower worldwide genetic diversity (respective number of genogroups: 4, 5, and 3) in comparison to CV-A9 (n = 10). The phylogenetic trees estimated with both 1D/VP1 and 3CD sequence data showed variations in the number of co-circulating lineages over the last 20 years among the four EV types. Despite the low number of genogroups in E-18, the virus exhibited the highest number of recombinant 3CD lineages (n = 10) versus 4 (E-5) to 8 (E-9). The phylogenies provided evidence of multiple transportation events between France and Tunisia involving E-5, E-9, E-18, and CV-A9 strains. Virus spread events between France and 17 other countries in five continents had high probabilities of occurrence as those between Tunisia and two European countries other than France. All transportation events were supported by BF values > 10. Inferring the source of virus transmission from phylogenetic data may provide insights into the patterns of sporadic and epidemic diseases caused by EVs.

Molecular characterization of coxsackievirus A21 in Shandong, China

Coxsackievirus A21 (CV-A21) is a rarely detected serotype belonging to the species Enterovirus C (EV-C). In this study, we report the isolation and genetic characterization of CV-A21 in Shandong Province, China, during 1997 to 2013. A total of 13 strains were obtained from surveillance of cases of acute flaccid paralysis (AFP) (n = 9) and from environmental sewage (n = 4). Sequence comparison of the VP1 genes revealed high nucleotide sequence similarity (94.1 % to 99.8 % identity) among these Shandong strains during the period of 17 years and 75.8 % to 98.5 % sequence identity to foreign strains. Bayesian phylodynamic evolutionary analysis of Shandong and global CV-A21 VP1 sequences revealed that the inferred CV-A21 ancestral sequence dated back to 1750 (1643-1841) and evolved with 2.943 × 10(-3) substitutions per site per year. Alignment of the deduced VP1 amino acid sequences revealed changes that might alter the hydropathicity of the encoded protein. The complete genome of one strain from 2013 was sequenced and evidence of recombination was detected by similarity plot and bootscanning analyses. This study describes the complete genome characterization and molecular epidemiology of CV-A21 in China and gives further insight into CV-A21 evolution.

Molecular epidemiology of coxsackievirus type B1

Coxsackievirus type B1 (CVB1) has emerged globally as the predominant enterovirus serotype and is associated with epidemics of meningitis and chronic diseases. In this report, the phylogeny of CVB1 was studied based on the VP1 sequences of 11 North African isolates and 81 published sequences. All CVB1 isolates segregated into four distinct genogroups and 10 genotypes. Most of the identified genotypes of circulating CVB1 strains appear to have a strict geographical specificity. The North African strains were of a single genotype and probably evolved distinctly. Using a relaxed molecular clock model and three different population models (constant population, exponential growth and Bayesian skyline demographic models) in coalescent analysis using the BEAST program, the substitution rate in CVB1 varied between 6.95 × 10(-3) and 7.37 × 10(-3) substitutions/site/year in the VP1 region. This study permits better identification of circulating CVB1, which has become one of the most predominant enterovirus serotypes in humans.

Species-specific transmission of novel picornaviruses in lemurs

The roles of host genetics versus exposure and contact frequency in driving cross-species transmission remain the subject of debate. Here, we used a multitaxon lemur collection at the Saint Louis Zoo in the United States as a model to gain insight into viral transmission in a setting of high interspecies contact. Lemurs are a diverse and understudied group of primates that are highly endangered. The speciation of lemurs, which are endemic to the island of Madagascar, occurred in geographic isolation apart from that of continental African primates. Although evidence of endogenized viruses in lemur genomes exists, no exogenous viruses of lemurs have been described to date. Here we identified two novel picornaviruses in fecal specimens of ring-tailed lemurs (Lemur catta) and black-and-white ruffed lemurs (Varecia variegata). We found that the viruses were transmitted in a species-specific manner (lesavirus 1 was detected only in ring-tailed lemurs, while lesavirus 2 was detected only in black-and-white ruffed lemurs). Longitudinal sampling over a 1-year interval demonstrated ongoing infection in the collection. This was supported by evidence of viral clearance in some animals and new infections in previously uninfected animals, including a set of newly born triplets that acquired the infection. While the two virus strains were found to be cocirculating in a mixed-species exhibit of ring-tailed lemurs, black-and-white ruffed lemurs, and black lemurs, there was no evidence of cross-species transmission. This suggests that despite high-intensity contact, host species barriers can prevent cross-species transmissions of these viruses.

IMPORTANCE

Up to 75% of emerging infectious diseases in humans today are the result of zoonotic transmission. However, a challenge in understanding transmission dynamics has been the limited models of cross-species transmission. Zoos provide a unique opportunity to explore parameters defining viral transmission. We demonstrated that ongoing virus transmission in a mixed lemur species exhibit was species specific. This suggests that despite high contact intensity, host species barriers contribute to protection from cross-species transmission of these viruses. While the combinations of species might differ, most zoological parks worldwide commonly feature mixed-species exhibits. Collectively, this report demonstrates a widely applicable approach toward understanding infectious disease transmission.

Genetic characterization of human coxsackievirus A6 variants associated with atypical hand, foot and mouth disease: a potential role of recombination in emergence and pathogenicity

Human coxsackievirus A6 (CVA6) is an enterically transmitted enterovirus. Until recently, CVA6 infections were considered as being of minor clinical significance, and only rarely aetiologically linked with hand, foot and mouth disease (HFMD) associated with other species A enteroviruses (particularly EV71 and CVA16). From 2008 onwards, however, CVA6 infections have been associated with several outbreaks worldwide of atypical HFMD (aHFMD) accompanied by a varicelliform rash. We recently reported CVA6-associated eczema herpeticum occurring predominantly in children and young adults in Edinburgh in January and February 2014. To investigate genetic determinants of novel clinical phenotypes of CVA6, we genetically characterized and analysed CVA6 variants associated with eczema herpeticum in Edinburgh in 2014 and those with aHFMD in CAV isolates collected from 2008. A total of eight recombinant forms (RFs) have circulated worldwide over the past 10 years, with the particularly recent appearance of RF-H associated with eczema herpeticum cases in Edinburgh in 2014. Comparison of phylogenies and divergence of complete genome sequences of CVA6 identified recombination breakpoints in 2A-2C, within VP3, and between 5' untranslated region and VP1. A Bayesian temporal reconstruction of CVA6 evolution since 2004 provided estimates of dates and the actual recombination events that generated more recently appearing recombination groups (RF-E, -F, -G and -H). Associations were observed between recombination groups and clinical presentations of herpangina, aHFMD and eczema herpeticum, but not with VP1 or other structural genes. These observations provided evidence that NS gene regions may potentially contribute to clinical phenotypes and outcomes of CVA6 infection.